Following the deaths of 18 stingray and three sharks, PETA is calling for the closure of the stingray touch tank at John Ball Zoo, MLive reports. 

The zoo announced July 8 that the animals had been found dead in the pool. According to MLive, the zoo is conducting an investigation. It is believed a mechanical malfunction caused the pool the animals were in to become low on oxygen. A back up system also failed to alert zoo staff.

PETA  Foundation Associate Director of Captive Animal Law Enforcement Rachel Mathews released the statement:

There are few exhibits deadlier than a touch tank, where sensitive aquatic animals are unable to escape a constant onslaught of groping hands that dirty and pollute the water with bacteria and where a single malfunction or mistake could suffocate and poison dozens of animals in one go. We saw it last night at the John Ball Zoo, and we saw it last year when an oxygen malfunction killed 54 cownose rays at the Brookfield Zoo. PETA is calling on the John Ball Zoo to take the only reasonable action here and close down the deadly touch tanks for good

PETA veterinarian Dr. Heather Rally sent a letter to John Ball Zoo, calling for them to close all touch tank exhibits at the zoo, writing, "Accidents happen, but that shouldn’t mean that animals pay with their lives."

Dr. Rally also writes:

Catastrophic failure is not the only source of suffering for animals held in touch tanks... Rays have a natural mucus coating on their skin that protects them from colonization by opportunistic pathogens. When human hands contact the rays’ skin, they can disrupt this basic protective mechanism and potentially inoculate the skin with a number of harmful foreign pathogens.

Andy McIntyre, the zoo's chief administrative officer, said in a statement,

"We are currently performing a thorough investigation to confirm the cause of this tragic incident as well as a comprehensive system review of all the zoo's aquatic life support systems,"